Integrated type optical node and optical information system using the same

ABSTRACT

This specification discloses an integrated type optical node comprising a substrate, a channel light waveguide formed on the substrate for connecting the transmission lines of an optical information system, an amplifying portion provided on the light waveguide for amplifying a light propagated through the waveguide, and a light branching-off portion provided on the light waveguide for coupling a light transmitter and/or a light receiver to the transmission lines. The specification also discloses an optical information system using such optical node.

This application is a continuation of application Ser. No. 07/718,927,filed Jun. 25, 1991, now U.S. Pat. No. 5,109,444, which is acontinuation of application Ser. No. 07/415,763, filed Oct. 2, 1989, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical node for coupling the transmissionlines of an optical information system to each end and an opticalinformation system using the same.

2. Related Background Art

In a bus type optical information system, as shown in FIG. 1 of theaccompanying drawings, optical nodes 102 are provided in a portion of anoptical fiber bus line 101 and an end instrument 103 having thetransmitting and receiving function is connected to each of the opticalnodes, whereby the information transmission between the ends is effectedthrough the bus line. As optical nodes used in such a bus system, therehave been proposed various types such as (1) the light receiving andemitting type and (2) the passive light branching-off type.

The light receiving emitting type mentioned under item (1) above is amethod in which after a light signal is converted into an electricalsignal, a light signal is again transmitted, and a light emitting andreceiving device is inserted on a bus line. This method, however, hassuffered from a problem such as the time delay of the signal due to thedelay of the reproduction time and in addition, a problem that thereproduction of a wavelength multiplexing signal is cumbersome.

On the other hand, the passive light branching-off type mentioned underitem (2) above is such that as shown in FIG. 2 of the accompanyingdrawings, a T-shaped branching-off coupler 104 is installed on a busline 101 and the introduction of a signal on the bus line and thetransmission of the signal to the bus line are effected to therebyrealize the information transmission between optical nodes. A receivingunit 106 and a transmitting unit 107 are connected under the T-shapedbranching-off coupler 104 through a Y-shaped branching-off coupler 105.However, in such a passive type optical branching-off node, theattenuation of light power due to the branch-off loss is remarkable, andthis has led to the basic problem that the number of optical nodesinstalled is limited.

Also, the dynamic range of the signal on the bus line becomes great dueto the branch-off coupling loss, and this has led to the problem thatthe burden for the performance of a photodetector becomes great.

In order to make up for such branch-off coupling loss, there is a methodof inserting an optical amplifier 108 onto the bus line and directlyamplifying the light signal, but this imparts a new coupling lossbecause of the increase in optical fiber coupling regions, and this inturn has led to the problem that a high amplification degree is requiredof the optical amplifier 108.

On the other hand, as similar examples in which an optical amplifier anda branching-off coupler are combined together, there have been proposedseveral, examples in which a compound type laser resonator isconstructed.

For example, in I. H. A. Fattah et al., "Semiconductor interterometriclaser", Appl. Phys. Lett. 41, 2, pp 112-114 (July, 1982), there isdescribed an interference type laser including a y branch-off as shownin FIG. 3 of the accompanying drawings. Also, in J. Salzman et. al.,"Cross coupled cavity semiconductor laser", Appl. Phys. Lett. 52, 10,pp. 767-769 (March, 1988), there is described an interference type laserincluding x branch-off as shown in FIGS. 4A and 4B of the accompanyingdrawings. Here, R₁ -R₄ designate resonating surfaces, and L₁ -L₄indicate the lengths of resonators.

Further, in Japanese Laid-Open Patent Application No. 62-145225, it isproposed to compensate for branch-off loss by the use of such abranching-off type laser.

However, it has not at all been conceived to utilize these lasers as thenode of an optical information system.

SUMMARY OF THE INVENTION

It is the object of the present invention to solve the above-notedproblems peculiar to the optical node according to the prior art and toprovide an efficient integrated type optical node which makes up forlight branch-off coupling loss and makes the coupling between atransmitter-receiver and a transmission line possible in bothdirections.

The above object of the present invention is achieved by an integratedtype optical node comprising a substrate, a channel light waveguideformed on said substrate for connecting the transmission line of anoptical information system, an amplifying portion provided on said lightwaveguide for amplifying a light propagated through said waveguide, anda light branching-off portion provided on said light waveguide forcoupling a light transmitter and/or a light receiver to saidtransmission line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptional view for illustrating an optical bus system.

FIG. 2 is a conceptional view of a passive branching-off type opticalnode which is an example of the prior art.

FIGS. 3, 4A and 4B are schematic views showing examples of aninterference type laser having branch-off in a laser amplifier.

FIG. 5 is a block diagram illustrating the optical node of the presentinvention.

FIG. 6 is a schematic view of an optical node according to a firstembodiment of the present invention.

FIG. 7 is a cross-sectional view of a laser amplifying portion in thefirst embodiment.

FIG. 8 is a schematic view of an optical node according to a secondembodiment of the present invention.

FIG. 9 is a schematic view showing a third embodiment of the presentinvention in which wavelength-multiplexed transmitting and receivingportions are made integral with each other.

FIGS. 10 to 12 are schematic views illustrating other forms of thebranching-off coupler portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 illustrates the basic concept of the present invention. In FIG.5, the reference numerals 1 and 2 designate optical fibers which areoptical bus lines, and the reference numeral 3 denotes an integratedoptical node according to the present invention which contains abidirectional branching-off coupler in an optical amplifier. Thereference numerals 6 and 7 designate a receiver and a transmitter,respectively, for end connection, the reference numerals 4 and 5 denoteoptical fibers for connecting the receiver 6 and the transmitter 7 tothe integrated optical node 3, the reference numeral 8 designates abranching-off coupler, and the reference numeral 9 denotes an isolator.

The operation of the integrated optical node 3 will hereinafter bedescribed.

When a multiplexed light signal is transmitted from the transmitter 7,it is coupled from the optical fiber 5 to the branch-off waveguide ofthe integrated optical node 3 and is separated into both directions,whereafter it is optically amplified, and the light signal istransmitted toward the optical fibers 1 and 2.

Design can be made such that the insertion loss of the coupling portionbetween the optical fibers and the optical node and the excessive lossof the bidirectional light branching-off coupler 8 are compensated forby an optical amplifying portion included in the integrated optical node3 and the light signal on the bus line assumes a substantially constantoutput level.

On the other hand, in the case of reception, the light signal which hascome from the optical fiber 1 or 2 which is a bus line is opticallyamplified in the integrated optical node 3. With that, the light signalwhich has come from any of the optical fibers 1 and 2 can also be partlyintroduced into the branch-off waveguide on the receiving side by thebranching-off coupler 8. The branched-off light signal is input to thereceiver 6 through the optical fiber 4 and is divided and detectedthereby, and giving and receiving of desired information can beeffected.

A part of the signal on the bus line always rectilinearly travelsthrough the branching-off coupler 8 and is amplified by the amplifyingportion, whereby the branch-off and coupling losses are compensated forand the signal level on the bus line is kept constant.

FIG. 6 shows the device construction of the integrated optical node ofthe present invention. The integrated optical node has a ridge-shapedwaveguide structure in which a GaAs/AlGaAs epitaxial layer is formed ona GaAs substrate 14 and stripe-like convex portions are formed on saidlayer. Laser amplifying portions 10a and 10b which are opticalamplifying portions are provided on the straight bus line, and directlyamplify the light signal on the bus line. These laser amplifyingportions may desirably be travelling wave type laser amplifiers which donot form resonators, and for that purpose, non-reflecting coatings13a-13d are applied to the input and output portions to eliminate anyunnecessary reflecting portion in the optical node. Also, in thebranching-off coupler 8, it is necessary to effect tapering to suppressunnecessary reflection.

The branching-off coupler 8 comprises a passive light waveguide whichdoes not provide a gain, and is formed by a compound of athree-branch-off waveguide and a two-branch-off (Y branch-off) waveguidein order to provide the bidirectional coupling of a reception sidebranch-off waveguide 11 and a transmission side branch-off waveguide 12.The feature of this branching-off coupler is that there is arectilinearly travelling portion toward the bus line and a light signalcan be transmitted in the both directions of the bus line from thebranch-off waveguides 11 and 12 for reception and transmission and thelight signal can be introduced from the both directions of the bus line.

Butt coupling is used for the coupling of the input and output port andthe optical fiber.

FIG. 7 is a cross-sectional view of the laser amplifying portion. InFIG. 7, the reference numeral 14 designates an n-GaAs substrate, thereference numeral 20 denotes an n-AlGaAs clad layer, the referencenumeral 21 designates a graded-index separate confinementheterostructure (GRIN-SCH) layer including a GaAs activated layer ofmultiplex quantum well (MQW) structure, the reference numeral 22 denotesa P-AlGaAs clad layer, the reference numeral 23 designates a GaAs caplayer, and the reference numerals 25 and 26 denote Au electrodes. Theridge is made by forming a pattern by photolithography, and thereafterby reactive ion beam etching. An SiNx layer 24 is piled, whereafter awindow is formed only in the upper portion of the ridge, and electrodeformation is effected. By biasing this laser amplifying portion by anelectric current of a threshold value or less, the amplification of theincident light can be accomplished.

In the foregoing description, the branching-off coupler 8 and thebranch-off waveguides 11 and 12 have been described as passivewaveguides, but it is also possible to make these portions into opticalamplifying portions.

FIG. 8 is a schematic view showing a second embodiment of the presentinvention. In the present embodiment, optical amplifying portions 30aand 30b disposed in the direction of the bus line are formed, andbranch-off waveguides 32 and 33 to the receiving portion and thetransmitting portion intersect the waveguide in the direction of the busline. A branching-off coupler 31 accomplishes branching-off coupling byforming a V-shaped groove in the portion of intersection. The ratio ofthe branching-off coupling can be adjusted by controlling thedistribution of the opto-electromagnetic field of the waveguide and thedepth of the groove. For the formation of such a groove, utilization canbe made of a minute working technique such as the etching by a Gafocused ion beam (FIB) or the etching by a reactive ion beam (RIB).

The other portions than the branching-off coupler 31 can be realized bya construction similar to that of the aforedescribed first embodiment.

The V-shaped branching-off coupler in the present embodiment differs inthe ratio of branch-off to the left and right branch-off waveguides 32and 33. Usually, in order to enhance the coupling of the receivingportion, the lower portion of the V-shape may preferably be disposedtoward the reception side branch-off waveguide 32. If the ratio ofbranch-off of the groove is -3 dB and the excessive loss is neglected,the ratio of branch-off to the reception side is -3 dB and the ratio ofbranch-off to the transmission side is -6 dB. Also, when light isincident on the upper portion (the open side) of the V-shape, there isreflection of -6 dB and therefore, in order to stabilize the frequencyon the transmission side, it is desirable to insert the isolator 9 asshown in FIG. 6.

In the above-described first and second embodiments, the optical nodeportion and the transmitting and receiving portions have been formed ondifferent chips and the connection therebetween has been effected. Inthe embodiment shown in FIG. 9, description will be made of a device inwhich the optical node portion and the transmitting and receivingportions are integrated on a single substrate. The transmitting portioncomprises distributed Bragg reflection type laser diodes (DBR-LD) 40aand 40b capable of transmitting two different wavelengths, awavelength-multiplexed light signal is transmitted by a Y wavesuperposing device 42. Light waves after Y wave combining further passthrough an isolator 43 and enter a branching-off coupler 44. Theisolator 43 can be realized by forming on a GaAs epitaxial film anepitaxial film consisting of CaMnTe by the molecular beam epitaxy (MBE)method, and constructing a reciprocal portion and a non-reciprocalportion, and a polarizing filter. Where the V-shaped branching-offcoupler 44 is used, the quantity of light reflected to the transmittingportion is great and the necessity of the isolator 43 increases. Also,in the branching-off coupler comprising a three-branch-off coupler and aY branch-off coupler as in the first embodiment, the influence of thereturn light of the receiving portion laser itself is small, but laseramplifiers 45a and 45b on the bus line effect travelling wave movementand therefore, it is necessary to eliminate the unnecessary reflectionon the DBR portion and the isolator 43 is important.

Next, on the reception side, the light signal from the bus line isamplified by the optical amplifier 45a or 45b, whereafter it is directedto a branch-off waveguide 47 by the branching-off coupler 44 and isBragg-diffracted by gratings 46a and 46b, and only a light signal of adesired wavelength is emitted to the slab waveguide portion on the sideof the ridge waveguide. The selected light signal is detected byindependent photodetectors 48a and 48b in conformity with the wavelengththereof. The layer construction of the photodetectors 48a and 48b isidentical to that of the optical amplifying portions 45a and 45b, andthese photodetectors can be made to operate as photodetectors by reversebias being applied thereto.

On the reception side, no isolator is incorporated and therefore, it isnecessary to make a contrivance such as obliquely setting a boundary 54as shown in FIG. 9, or tapering the boundary, in order to suppressunnecessary reflection in each level difference portion. Of course, ifisolators are installed on both branches, an improved performance can beexpected.

The optical amplifiers and the branching-off coupler in the presentembodiment have a wide wavelength band and therefore are considered tobe useful as the integrated optical node of a wavelength-multiplexedoptical bus system.

Besides the above-described embodiments, various constructions may beconceived as the construction of the bidirectional branching-off typecoupler portion. FIG. 10 shows a construction in which a dual gratingstructure 50 is formed in the portion of intersection between waveguidesto thereby realize bidirectional branching-off coupling. The grating canbe locally formed by the electron beam exposure method or the like. InFIGS. 10 to 12, for simplicity, the other constituents such as theoptical amplifying portion and the optical fiber are omitted.

FIG. 11 shows a construction in which two T-shaped branching-offcouplers 51a and 51b are combined together to accomplish bidirectionalcoupling to the transmitting and receiving portions. Such T-shapedcoupler can be provided by removing the central portion of a T-shapedwaveguide in the form of a prism. In the prism-like portion, the guidedlight is designed to be subjected to total reflection.

FIG. 12 shows a construction in which two T-shaped branching-offcouplers 52a and 52b of the directional coupler type are combinedtogether to accomplish bidirectional coupling to the transmitting andreceiving portions.

Branching-off devices of the directional coupler type and the gratingdiffraction type have wavelength dependency and therefore, it will benecessary to adjust the coefficient of coupling so as to have anappropriate wavelength selection width in the wavelength multiplexingarea used. This poses no problem in a bus system of a single wavelengthDesignated by 53 is a laser amplifying portion.

As described above, in the integrated optical node of the presentinvention, a laser amplifying area for optical amplification and abranching-off coupler portion for bidirectionally accomplishing thecoupling to a plurality of waveguides for the coupling to thetransmitter and the receiver are provided in a channel waveguide,whereby it has become possible to compensate for the light branching-offand coupling loss as an optical node for an optical information systemand bidirectionally accomplish the coupling between the transmitter, thereceiver and the transmission line. Also, by using the integratedoptical node of the present invention, the light power level on thetransmission line can be made substantially equal and the multistageconnection of the optical node becomes possible and also, the dynamicdetection range of the photodetector can be made small and a higherperformance of the information system can be achieved.

Further, by making the optical branching-off portion and the opticalamplifying portion and the transmitting and receiving portions integralwith one another, the number of the complicated coupling portionsbetween the optical fiber and the waveguide can be reduced, and this iseffective for making the element compact.

Besides the above-described embodiments, the present invention permitsvarious applications. The present invention covers all of suchapplications without departing from the scope of the invention asdefined in the appended claims.

We claim:
 1. An integrated type optical node comprising:a substrate; alight waveguide formed on said substrate and coupled to transmissionlines of an optical information system; first and second laser lightsources integrated with said light waveguide formed on said substratefor emitting lights having different wavelengths from each other; firstand second photodetectors integrated with said light waveguide formed onsaid substrate for receiving lights having different wavelengths fromeach other; and a light branching-off portion for coupling the lightsemitted from said first and second laser light sources to saidtransmission lines through said light waveguide and for coupling a partof light transmitted in said transmission lines to said first and secondphotodetectors through said light waveguide.
 2. An integrated typeoptical node according to claim 1, wherein said first and second laserlight sources respectively comprise distributed Bragg reflection typelaser diodes.
 3. An integrated type optical node according to claim 1,wherein said branching-off portion comprises two three-forked branch-offpaths and two-forked branch-off paths.
 4. An integrated type opticalnode according to claim 1, wherein said branching-off portion comprisesa V-shaped groove formed on said wavelengths.
 5. An integrated opticalnode according to claim 1, where in said branching-off portion comprisesa dual grating structure formed on said waveguide.
 6. An integrated typeoptical node according to claim 1, wherein said branching-off portioncomprises a prism-like removed portion formed on said waveguide.
 7. Anintegrated type optical node according to claim 1, wherein saidbranching-off portion comprises two T-shaped branching-off couplers of adirectional coupler type.
 8. An integrated type optical node accordingto claim 1, further comprising an amplifying portion formed on a portionof said waveguide for amplifying light transmitted in said waveguide. 9.An integrated type optical node according to claim 8, where saidamplifying portion comprises a laser amplifier for effecting operationof a traveling wave type.
 10. An integrated type optical node accordingto claim 1, further comprising an isolator provided between saidbranching-off portion and said first and second laser light sources. 11.An optical information system comprising:a plurality of integrated typeoptical nodes; and a plurality of transmission lines for effectingtransmission of light signals between said plurality of integrated typeoptical nodes; wherein each of said plurality of integrated type opticalnodes comprises: a substrate; a light waveguide formed on said substrateand coupled to said transmission lines; first and second laser lightsources integrated with said light waveguide formed on said substratefor emitting lights having different wavelengths from each other; firstand second photodetectors integrated with said light waveguide formed onsaid substrate for receiving lights having different wavelengths fromeach other; and a light branching-off portion for coupling the lightsemitted from said first and second laser light sources to saidtransmission liens though said light waveguide and for coupling a partof light transmitted in said transmission lines to said first and secondphotodetectors through said light waveguide.
 12. An optical informationsystem according to claim 11, wherein said first and second laser lightsources respectively comprise distributed Bragg reflection type laserdiodes.
 13. An optical information system according to claim 11, whereinsaid branching-off portion comprises two three-forked branch-off pathsand two-forked branch-off paths.
 14. An optical information systemaccording to claim 11, wherein said branching-off portion comprises aV-shaped groove formed on said waveguide.
 15. An optical informationsystem according to claim 11, wherein said branching-off portioncomprises a dual grating structure formed on said waveguide.
 16. Anoptical information system according to claim 11, wherein saidbranching-off portion comprises a prism-like removed portion formed onsaid waveguide.
 17. An optical information system according to claim 11,wherein said branching-off portion comprises two T-shaped branching-offcouplers of a directional coupler type.
 18. An optical informationsystem according to claim 12 further comprising an amplifying portionformed on a portion of said waveguide for amplifying light transmittedin said waveguide.
 19. An optical information system according to claim18, wherein said amplifying portion comprises a laser amplifier foreffecting operation of a traveling wave type.
 20. An optical informationsystem according to claim 11 further comprising an isolator providedbetween said branching-off portion and said first and second laser lightsources.